It is known that viruses need the host's mechanisms of synthesis and energy to multiply themselves. It is also well known that the beginning of a viral infectious disease chiefly involves the adhesion of the viral particles to specific structures present on the membrane of the host cell. As a result of these early interactions, the intracellular phase of the virus and its subsequent replication or the integration in the cellular genome occurs.
When the virus multiplies, the host cell proceeds towards lysis and the infection spreads. In contrast, when the viral genome is integrated into the cell genome, avoiding the host defense, the host cell is not lysed as long as the viral genome remains integrated without multiplying. In particular cases, the integrated viral DNA can start a new replication cycle, causing cell lysis and, therefore, infections recur because of the production of mature viral particles. The peculiar life cycle of a virus does not easily allow one to find substances with antiviral properties that prevent the early phase of the interaction of virus-cells without being, at the same time, toxic towards the host cell.
Herpesviridae is a family of virus that cause acute and recurrent diseases. In particular, Herpes simplex virus type 1 (HSV1), a neurodermotrophic virus that afflicts 60-90% of the adult population and, after the primary infection, often becomes clinically silent in the host organism, and can remain in the skin cells and in the endings of nervous cells in a latent state. It is responsible for the events of primary gingival stomatitis, of recurrent labial Herpes, of eczema herpeticum,of herpetic keratitis and of supra-umbilical skin infections. In fact, after skin-breaking events like exposure to sunlight, fever or emotional stress, the virus can reactivate and cause the appearance of painful and boring skin vesicles that remain for some days even when after the disappearance of the skin-breaking event. Preferential sites of localization are lips and rarely genitals, contrary to that observed with Herpes simplex virus type 2 which is responsible for genital infections.These infections involve the genitalia, anorectum and oropharynx. A large study of patients with genital herpes suggested that recurrences typically occur 5-8 times a year.
Only sunlight filters are used for the prevention towards Herpes simples type 1 on the lips, while the antiviral therapy is based on chemotherapeutics that inhibit the viral replication of the Herpes simplex virus. However, the filters only prevent the viral reactivation after sunlight exposure and the chemotherapeutics are either potentially toxic and their prolonged use is often associated with serious effects such as anemia, neutropenia and irreversible testicular damage.
Another example is represented by Rhinovirus, ethiological agents of the common cold, for which a decisive therapy does not exist because of the 115 different antigenic varieties that exist which prevents the formulation of an effective vaccine. On the other hand, the relative harmlessness of the above mentioned viral infections does not suggest the therapeutic utilization of antiviral drugs even though they possess some toxicity towards the host organism.
With the aim to inhibit the viral replication, an approach can be represented by the inhibition of the early virus-cell interactions thus inhibiting the internalization of the infectious agent or by the inactivation of the enzymes necessary for viral replication.
Concerning the first approach, that is the inhibition of the early virus-cell interactions, many substances have been tested in the last years but only some of them carry this activity through specific bonds both to cell receptors and to viral anti-receptors.
Recently, an antiviral function of lactoferrin has been demonstrated, a glycoprotein able to bind 2 atoms of Fe.sup.3+ per molecule. The antiviral function of lactoferrin, firstly attributed to its iron deprivation capability, may be, on the contrary, due to a specific binding with the host surface in its N-terminus in a region distinct from ther iron binding sites. In fact, it has been demonstrated that lactoferrin (human and bovine) specifically binds to heparin sulfate, a ubiquitous proteoglycan, multifunctional constituent of mammalian cell membranes and of extracellular matrix. This component and other glycosaminoglycans may act as receptors for some enveloped viruses, including HSV1 and HIV. It can be inferred that lactoferrin is able to selectively inhibit the early interactions HSV1-host cell and, consequently, is able to inhibit the internalization of the virus.
In physiological conditions, such as in the common media for cell cultures, lactoferrin is partially saturated in its iron binding sites. In this condition, lactoferrin assumes a "close" conformation that allows the binding to the surface receptorial structures of the host cells and a greater resistance to the proteases. This binding between saturated lactoferrin and the receptor, while competitively inhibiting the adsorption of the virus to the cell, facilitates the penetration of Fe.sup.3+ ions inside the cell. The latter event could prevent a therapeutic utilization of lactoferrin as antiviral agent, since the iron transported into the cell influences the replication of the virus particles already present inside the cells. In fact, even with different viruses and experimental models and sometimes with conflicting results, it is well demonstrated that iron and other metals are important in the catalytic activity of viral ribonucleotide reductase enzymes. In fact, metal chelating substances are reported to be inhibitors of viral ribonucleotide rcductascs including those codified by Herpesviris, while they do not influence cellular reductases.
Among the above-stated chelators, desferrioxamine methariesulfonate, a hydroxamic siderophore produced by Streptomyces pilosus and for a long time utilized in the therapy of human hemochromatosis following hemolytic diseases, appears to be very active, being able to chelate Fe.sup.3+ ions with high affinity and, with lower affinity, other metal ions.
The therapeutic utilization of these chelating compounds either in apo or different saturated forms as antiviral agents alone was, until now, not possible since the above-mentioned substances, while slowing down the viral multiplication phase, did not prevent the penetration of the virus into the cell. The cells would therefore be infected by the virus, anyhow.
The therapeutic model, described in the present invention is based on the synergistic antiviral activity exerted by lactoferrin (or serotransferrin or ovotransferrin) and desferrioxamine methanesulfonate (or other low molecular weight metal ion chelators) both compounds being in apo form or in iron, manganese and zinc saturated forms. The antiviral activity of this preparation, heretofore not described in literature, is remarkably higher than that shown with the two separate components because their activity is exerted on two separate phases of the viral cycle (adsorption and replication). Therefore, it can be inferred that therapeutic advantage of such a preparation is greater towards viral infections in comparison with the currently used antiviral pharmacological therapies based on the inhibition of viral replicative mechanisms and that are characterized by toxicity towards the host organism.
Lactoferrin, possessing very low or no toxicity, and the chelate desferrioxamine methanesulfonate, already utilized in human hemochromatosis therapy, can be administered by topical and systemic routes against viral infections concerning skin and mucous membranes such as nasal, oropharyngeal, intestinal, bronchial and genital membranes0.